Motion compensation system for under water sonar systems

ABSTRACT

An underwater buoyancy apparatus for compensating for wave induced vertical and/or horizontal motion, particularly in sonar devices deployed from nautical platform. The underwater buoyancy apparatus is slidably connected along a tether between a nautical platform and an underwater sonar device. The underwater buoyancy apparatus contains a volume of air and/or water which can be changed to thereby alter the underwater buoyancy apparatus&#39;s depth in a body of water, in response to vertical and/or horizontal motion the nautical platform.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to underwater sonar systems. More particularly it relates to an underwater buoyancy apparatus and method for compensating for environmentally induced vertical and/or horizontal motion of underwater sonar devices deployed from surface ships and other surface platforms.

2. Description of the Related Art

The detection of submarines at a safe standoff distance from a protected surface ship is important in military applications. The “dipping” of active sonar devices deployed from manned helicopters has been one of the primary methods of detecting, tracking and prosecuting submarines for many years.

A dipping sonar device essentially includes a grouping of active transmit transducers, passive receive hydrophones, and associated circuitry deployed from a helicopter to some depth in the water column (i.e. dipped), by means of a cable and reel mechanism. The transducers, when stimulated by an electric current, emit acoustic energy at a prescribed frequency and in a pre-determined beam pattern. The transmitted acoustic energy radiates outward from the transducers until it is reflected back from an object in the water. The passive receive hydrophones receive the returned acoustic signal, transpose the acoustic energy to an electric signal, and pass the signal up the cable for further processing.

The helicopter hovers at a precise altitude during the entire cycle, maintaining the sonar unit at a stable pre-determined depth. Since the helicopter is hovering above the water surface, and the dipping sonar unit is deployed several hundred feet below the surface, the sonar device is divorced from motion effects induced by the body of water, such as wave-induced motion.

Recent developments with unmanned surface vehicles (USVs) and the requirement for the capability to conduct anti-submarine warfare in disputed waters near hostile nations have resulted in interest in conducting anti-submarine warfare search, detect, and prosecute operations from unmanned surface vehicles deployed over-the-horizon from the host ship.

Deploying a dipping sonar unit from an unmanned surface vehicle is similar to deploying a dipping sonar from a hovering helicopter, except the USV is not separated from the water surface. This results in two fundamental differences in operation of the USV as compared to the helicopter. The USV is subject to vertical motion induced by wave action, and to horizontal motion induced by wind and current.

Extraneous acoustic energy, or noise, sensed by the passive receive hydrophones decreases the hydrophone's capability to sense the reflected acoustic signal reflected from the target of interest. This results in the necessity to either increase the signal strength of the transmitted signal above some threshold determined by the noise sensed by the hydrophones, or to reduce the noise level. An increasing of the transmitted signal is limited by the power requirements and size of the transducers relative to the power and lift capability of the host platform, as well as the cavitation limits and reverberation limits of the water environment. Thus, transmitted power levels are limited. Reduction of noise level is achievable only for those noise sources within the control of the sonar device to envelop.

In the case of a dipping sonar device deployed from a USV, vertical motion of the receive hydrophones caused by wave induced motion of the USV causes flow noise in the immediate vicinity of the hydrophone. Depending on the vertical velocity and acceleration, this flow noise can be of a magnitude sufficient to blank the hydrophone from receiving any signal.

Lateral motion of the USV caused by wind or current results in the array being pulled to a cant angle such that both the transmitted beams and the receive beams would be at some angle off horizontal. To minimize degradation in performance caused by this cant angle, the USV must continuously maneuver to maintain the cable and the deployed sonar device as near to vertical as possible. This continuous maneuvering results in significant propulsion noise being entrained in the water above, and in relatively close proximity to, the sonar device.

Accordingly, the present invention solves the above-mentioned problems by providing a method of compensating for the surface wave induced vertical motion of the sonar device, and to eliminate the necessity for an unmanned surface vehicle to maintain verticality with the sonar device. This is accomplished by supporting the underwater sonar device from an underwater buoyancy apparatus at some depth below the water's surface.

SUMMARY OF THE INVENTION

The invention provides a nautical system comprising:

a) a nautical platform adapted for positioning on or within a body of water;

b) an underwater buoyancy apparatus connected to the nautical platform via at least one tether, which underwater buoyancy apparatus comprises:

a housing defining an inner buoyancy chamber, which buoyancy chamber is capable of containing a volume of air and/or water, and wherein the housing comprises at least one air valve capable of allowing air into and/or out of the inner buoyancy chamber and at least one flood port capable of allowing water into and/or out of the inner buoyancy chamber;

c) an underwater sonar device connected to the underwater buoyancy apparatus via at least one tether, such that a distance between the underwater buoyancy apparatus and the sonar device is adjustable, which sonar device is capable of transmitting and/or receiving acoustic sonar signals; and

d) a control arrangement for controlling the at least one valve and/or the at least one flood port of the underwater buoyancy apparatus.

The invention further provides an underwater buoyancy apparatus comprising a housing defining an inner buoyancy chamber, which buoyancy chamber is capable of containing a volume of air and/or water, and wherein the housing comprises at least one air valve capable of allowing air into and/or out of the inner buoyancy chamber and at least one flood port capable of allowing water into and/or out of the inner buoyancy chamber; which underwater buoyancy apparatus further comprises at least one tether for connecting the underwater buoyancy apparatus to a nautical platform; and which underwater buoyancy apparatus further comprises at least one tether for connecting the underwater buoyancy apparatus to an underwater sonar device such that a distance between the underwater buoyancy apparatus and the underwater sonar device is adjustable.

The invention still further provides a method for adjusting the position of an underwater sonar device which comprises:

I) deploying a nautical system into a body of water, which nautical system comprises:

-   -   a) a nautical platform adapted for positioning on or within a         body of water;     -   b) an underwater buoyancy apparatus connected to the nautical         platform via at least one tether, which underwater buoyancy         apparatus comprises:     -   a housing defining an inner buoyancy chamber, which buoyancy         chamber is capable of containing a volume of air and/or water,         and wherein the housing comprises at least one air valve capable         of allowing air into and/or out of the inner buoyancy chamber         and at least one flood port capable of allowing water into         and/or out of the inner buoyancy chamber;     -   c) an underwater sonar device connected to the underwater         buoyancy apparatus via at least one tether, such that a distance         between the underwater buoyancy apparatus and the sonar device         is adjustable, which sonar device is capable of transmitting         and/or receiving acoustic sonar signals; and     -   d) a control arrangement for controlling the at least one valve         and/or the at least one flood port of the underwater buoyancy         apparatus;         II) accepting sufficient amounts of air and/or water into the         inner buoyancy chamber such that underwater buoyancy apparatus         maintains a substantially fixed depth within the body of water;         and         III) controllably adjusting the depth of the underwater buoyancy         apparatus to thereby compensate for the effects of movement of         the nautical platform on the underwater sonar device by         conducting at least one of steps (i) and (ii):     -   i) lowering the underwater buoyancy apparatus within the body of         water, by releasing air from within the buoyancy chamber via the         at least one air valve, and taking water into the buoyancy         chamber via the at least one flood port; and/or     -   ii) raising the underwater buoyancy apparatus within the body of         water, by taking air into the buoyancy chamber via the at least         one air valve, and releasing water from within the buoyancy         chamber via the at least one flood port.

The invention still further provides a method for the emergency recovery of an underwater buoyancy apparatus and a sonar device which are part of a nautical system, the method comprising;

I) deploying a nautical system into a body of water, which nautical system comprises:

-   -   a) a nautical platform adapted for positioning on or within a         body of water;     -   b) an underwater buoyancy apparatus connected to the nautical         platform via at least one tether, which underwater buoyancy         apparatus comprises:     -   a housing defining an inner buoyancy chamber, which buoyancy         chamber is capable of containing a volume of air and/or water,         and wherein the housing comprises at least one air valve capable         of allowing air into and/or out of the inner buoyancy chamber         and at least one flood port capable of allowing water into         and/or out of the inner buoyancy chamber;     -   c) an underwater sonar device connected to the underwater         buoyancy apparatus via at least one tether, such that a distance         between the underwater buoyancy apparatus and the sonar device         is adjustable, which sonar device is capable of transmitting         and/or receiving acoustic sonar signals; and     -   d) a control arrangement for controlling the at least one valve         and/or the at least one flood port of the underwater buoyancy         apparatus; and     -   e) a tether connection sensor capable of sensing a loss of         tether continuity between the nautical platform and the sonar         device; and     -   f) a depth control system comprising:         -   i) an underwater buoyancy apparatus depth sensor for sensing             the depth of the underwater buoyancy apparatus and an             underwater sonar device depth sensor for sensing the depth             of the underwater sonar device and which underwater buoyancy             apparatus depth sensor and sonar device depth sensor are             each capable of sending a data signal to a depth control             processor, which data signal provides depth and/or position             data of the underwater buoyancy apparatus and the underwater             sonar device, respectively, to a depth control processor;             and         -   ii) a depth control processor capable of sending and             receiving data signals and/or action signals to and from the             underwater buoyancy apparatus depth sensor, the sonar device             depth sensor, the at least one air valve, and/or the at             least one flood port, and which depth control processor is             further capable of controlling the at least one air valve             and/or the at least one flood port; and     -   g) a locking sheave system through which the at least one tether         is routed, which locking sheave system is positioned between the         nautical platform and the underwater buoyancy apparatus, and         which locking sheave system is capable of locking to and         unlocking from the at least one tether at adjustable positions         along the at least one tether to thereby maintain a         substantially fixed distance between the sonar device and the         underwater buoyancy apparatus, and/or adjust the distance         between the underwater buoyancy apparatus and the sonar device;         II) generating a first command signal from the depth control         sensor, in response to a loss of tether continuity signal from         the tether connection sensor, such that the locking sheave         system locks;         III) generating a second command signal from the depth control         sensor, thereby directing the opening of the at least one air         valve of the underwater buoyancy apparatus in response to a loss         of tether continuity signal; and         IV) controllably forcing air into the underwater buoyancy         apparatus such that underwater buoyancy apparatus is raised to         the surface of the body of water in response to the loss of         tether continuity signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of a nautical system of the present invention.

FIG. 2 illustrates a block diagram of a buoyancy control algorithm of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a nautical system, shown in FIG. 1, which nautical system 1 comprises a nautical platform 3, an underwater buoyancy apparatus 5 connected to the nautical platform, and an underwater sonar device 7 connected to the underwater buoyancy apparatus.

The nautical platform 3 may comprise any suitable object, device, vessel, or the like adapted for positioning on or within a body of water 9. Examples of suitable nautical platforms nonexclusively include buoys, rafts, tanks, surface vessels, underwater vessels, manned or unmanned vehicles such as boats, ships, submarines, and the like. In one preferred embodiment of the invention, the nautical platform comprises a boat. Preferably the nautical platform comprises at least one tether connection point 11 for connecting to at least one tether as described below. In a preferred embodiment, the tether connection point 11 comprises a reeling mechanism for deployment and retrieval of the underwater buoyancy apparatus and sonar device in relation to the nautical platform 3.

The underwater buoyancy apparatus 5 is connected to the nautical platform 3, preferably via at least one tether 13. The underwater buoyancy apparatus 5 preferably comprises a housing defining an inner buoyancy chamber 17 capable of containing a volume of air and/or water, as shown. The housing may comprise any suitable material in any suitable shape and size determined by those skilled in the art, such that the inner buoyancy chamber 17 may be substantially pressure tight, water tight, and air tight. Examples of suitable housing materials nonexclusively include metal, plastic, or the like. The housing preferably comprises a sufficient diameter and length such that the inner buoyancy chamber 17 is capable of containing a suitable volume of air and/or water to provide sufficient buoyancy to support the displaced weight of the underwater buoyancy apparatus 5, the weight of a sonar device 7, and the weight of the at least one interconnecting tether 13.

In one embodiment, the housing further comprises at least one tether connection point 19 which preferably includes a slidable connector such as a loop, a pulley or series of pulleys, a lockable sheave mechanism, or the like, for slidably connecting the at least one tether to the underwater buoyancy apparatus 5. Preferably, the tether connection point 19 comprises a locking sheave system, as described below, which comprises at least one mechanical lockable sheave mechanism, a brake assembly, and/or a pulley or series of pulleys with lockable shafts, such that at least one tether 13 of the nautical system may be routed through the locking sheave system 35, for slidably connecting at least one tether 13 to the underwater buoyancy apparatus 5. In a further embodiment, the housing of the underwater buoyancy apparatus 5 may comprise an internal tether tube 34 capable of allowing the at least one tether 13 to slidably pass through all or a portion of the housing. As shown in the embodiment of FIG. 1, the underwater buoyancy apparatus 5 includes an internal tether tube 34 which allows at least one tether 13 to pass all the way through underwater buoyancy apparatus 5.

The housing preferably further comprises at least one air valve 21 capable of allowing air into and/or out of the inner buoyancy chamber 17, and at least one flood port 23 capable of allowing water into and/or out of the inner buoyancy chamber 17. The flowing of air and/or water into and out of the inner buoyancy chamber 17 serves to alter of depth of the underwater buoyancy apparatus 5 within a body of water 9. This allows for sufficient internal volume within the buoyancy chamber 17 for changes in the air and/or water volume to compensate for vertical forces on the underwater buoyancy apparatus 5 and sonar device 7. Such vertical forces might be induced by sea surface motion and/or wind acting on the nautical platform or directly on the underwater buoyancy apparatus.

The releasing of air from within the buoyancy chamber 17 via the at least one air valve 21 and/or the taking in of water into the buoyancy chamber 17 via the at least one flood port 23 serves to lower the underwater buoyancy apparatus 5 within the body of water 9. Contrarily, the taking in of air into the buoyancy chamber 17 via the at least one air valve 21 and/or the releasing of water from within the buoyancy chamber 17 via the at least one flood port 23 serves to raise the underwater buoyancy apparatus 5 within the body of water 9. The at least one air valve 21 and/or at least one flood port 23 are preferably electronically controlled, and are preferably further capable of sending and/or receiving signals such as data and/or command signals to and from a controller such as a control arrangement 25, described below.

The at least one air valve 21 is preferably present at or near a top end of the housing of the underwater buoyancy apparatus 5. The at least one flood port 23 is preferably present at or near a bottom end of the housing of the underwater buoyancy apparatus 5. The at least one flood port 23 is preferably capable of opening and closing, either automatically or in response to a signal from a control arrangement 25 described below, to allow water into and out of the inner buoyancy chamber 17. Alternatively, the at least one flood port can be arranged such that it allows for substantially free communication between the internal water volume and the outside body of water.

The at least one air valve 21 preferably comprises at least one vent valve capable of expelling or releasing air from the buoyancy chamber. When the vent valve is opened, preferably in response to a signal from a control arrangement 25 as discussed below, air is released from the buoyancy chamber 17 via the vent valve. As the air pressure in the buoyancy chamber is reduced, water is taken into the buoyancy chamber 17 via the at least one flood port 23. With an increased volume of water and decreased volume of air within the buoyancy chamber 17, the buoyancy of the underwater buoyancy apparatus 5 is thereby decreased and it sinks to a lower depth within the body of water 9. When the vent valve is closed, preferably is response to a signal from the control arrangement 25 as discussed below, the air volume in the buoyancy chamber 17 is held substantially constant. Thus, water can no longer enter the buoyancy chamber 17, and the underwater buoyancy apparatus 5 is maintained at a substantially fixed depth within the body of water 9.

The at least one air valve 21 preferably comprises at least one blow valve capable of injecting or taking air into the buoyancy chamber via an air source. In such an embodiment, the blow valve is preferably connected to an air source 27 such as a high-pressure air tank. When the blow valve is opened, preferably in response to a signal from a control arrangement 25 as discussed below, pressurized air, or air of a pressure in excess of the existing external sea pressure, passes from air source 27 into the buoyancy chamber 17 via the blow valve. As the air pressure within the buoyancy chamber is increased, water is expelled from the buoyancy chamber 17 via the at least one flood port 23. With a decreased volume of water and increased volume of air within the buoyancy chamber 17, the buoyancy of the underwater buoyancy apparatus 5 is increased and it rises to a shallower depth within the body of water 9. When the blow valve is closed, preferably in response to a signal from the control arrangement 25 discussed below, the air volume in the buoyancy chamber 17 approaches a pressure equilibrium with external sea pressure. At or near such equilibrium, the air volume in the buoyancy chamber 17 is held substantially constant. Thus, water can no longer exit the buoyancy chamber 17, and the underwater buoyancy apparatus 5 is maintained at a substantially fixed depth.

The nautical system 1 further comprises underwater sonar device 7 connected to the underwater buoyancy apparatus 5 via at least one tether 13, such that a distance between the underwater buoyancy apparatus 5 and the sonar device 7 is adjustable. The sonar device 7 may comprise any suitable device that is capable of transmitting and/or receiving acoustic sonar signals in water and/or air. Such sonar devices are well known in the art for their use in military operations and the like. The sonar device 7 preferably comprises at least one tether connection point 29 for connecting to at least one tether 13.

In a preferred embodiment, the underwater buoyancy apparatus 5 connected to the nautical platform 3 via at least one tether 13, and the underwater buoyancy apparatus 5 is connected to the sonar device 7 via at least one tether 13. The at least one tether 13 between the nautical platform 3 and the underwater buoyancy apparatus 5 may or may not be continuous with the at least one tether 13 between the underwater buoyancy apparatus 5 and the underwater sonar device 7. Furthermore, the underwater buoyancy apparatus 5 is preferably positioned between the nautical platform 3 and a sonar device 7, such that it is slidably connected along the at least one tether 13 between the nautical platform 3 and a sonar device 7. Preferably, the distance between the nautical platform 3 and the underwater buoyancy apparatus 5 is adjustable, and/or the distance between the underwater buoyancy apparatus 5 and the underwater sonar device 7 is adjustable.

The at least one tether 13 is preferably sufficiently slack between the nautical platform 3 and the underwater buoyancy apparatus 5 such that a horizontal and/or vertical motion of the nautical platform 3 does not impart a substantial vertical or horizontal force to the underwater buoyancy apparatus 5. Examples of suitable tethers nonexclusively include rope, chain, cabling, wire, and the like. In one preferred example, the at least one tether 13 comprises a communications cable. Such communications cables are preferably capable of transmitting data signals between various components of the nautical system. Suitable communications cables are well known in the field of sonar devices.

The nautical system 1 preferably further comprises a control arrangement 25 for controlling the generation and transmission of signals, such as data signals, action signals, command signals, and/or control signals between various components of the nautical system. The control arrangement 25 may be present in the form of an internal or external feature of any component of the nautical system 1, or of any other remotely or physically connected mechanism of the nautical system. The control arrangement 25 may be attached to any or all such components of the nautical system 1 in any suitable manner, such as a wired or wireless connection. In one preferred embodiment, the control arrangement 25 is present on or within the housing of the underwater buoyancy apparatus 5.

The control arrangement 25 is preferably capable of controlling the opening and/or closing of the at least one air valve 21 and/or the at least one flood port 23 of the underwater buoyancy apparatus 5. In one embodiment, the control arrangement 25 comprises an air controller for the at least one air valve, for controlling a flow of air into and/or out of the inner buoyancy chamber. In another embodiment, the control arrangement 25 comprises a water controller for the at least one flood port, for controlling a flow of water into and/or out of the inner buoyancy chamber.

In a preferred embodiment, the control arrangement 25 comprises a depth control system. The depth control system preferably comprises various sensors, connections, and processors of the nautical system 1. Preferably, the depth control system comprises depth sensors capable of sending data signals to a depth control processor of the depth control system, and which data signals include depth and/or position data of at least one component of the nautical system 1. In a preferred embodiment, the depth control system comprises an underwater buoyancy apparatus depth sensor 31 for sensing the depth of the underwater buoyancy apparatus 5, and which underwater buoyancy apparatus depth sensor 31 is capable of sending a data signal to a depth control processor of the depth control system, wherein the data signal provides depth and/or position data of the underwater buoyancy apparatus 5. In a further preferred embodiment, the depth control system comprises an underwater sonar device depth sensor 33 for sensing the depth of the underwater sonar device 7, and which sonar device depth sensor 33 is capable of sending a data signal to a depth control processor, wherein the data signal provides depth and/or position data of the underwater sonar device 7.

The depth control system comprises a depth control processor capable of sending and/or receiving signals such as data signals, action signals, command signals, and/or control signals to various components of the nautical system 1. Preferably, the depth control processor is capable of sending and/or receiving such signals to and from the underwater buoyancy apparatus depth sensor 31, the sonar device depth sensor 33, the at least one air valve 21, the at least one flood port 23, and the locking sheave system 35, described below. The depth control processor is further capable of controlling the opening and closing of the at least one air valve 21 and/or the at least one flood port 23 as described above.

The depth control processor preferably comprises a computer processor and/or any other suitable components or materials known in the art capable of performing the calculation, processing, sending and/or receiving of signals such as data signals, action signals, command signals, and/or control signals to and from the various components of the inventive nautical system 1. The depth control processor is preferably capable of calculating the sensed depth of and/or determining a targeted ordered depth of the underwater buoyancy apparatus 5, the underwater sonar device 7, and/or other components of the nautical system 1.

The nautical system 1 may further comprise various components useful in the performance of underwater sonar operations. Examples of such components nonexclusively include one or more various depth sensors, proximity sensors, velocity sensors, accelerometers, signal receivers, signal transmitters, data processors and calculators, and combinations or groups thereof. Additional useful components comprise wireless or wired electrical connections between the nautical platform 3, the underwater buoyancy apparatus 5, the sonar device 7, and/or other remote or attached mechanisms.

The nautical system may further comprise at least one tether connection sensor, capable of sensing a break or other loss in continuity of a tether connection between any components of the nautical system. In one preferred embodiment, the tether connection sensor is capable of sensing a break or other loss in continuity of a tether or tethers connected to the sonar device 7.

The nautical system may further comprise a vertical velocity sensor 36, such as an underwater buoyancy apparatus vertical velocity sensor for sensing the vertical velocity of the underwater buoyancy apparatus 5. The underwater buoyancy apparatus vertical velocity sensor 36 is preferably capable of sending a data signal to the depth control processor, which data signal provides vertical velocity data of the underwater buoyancy apparatus 5 to the depth control processor. The depth control processor may then send a command signal, in response to the vertical velocity data signal, to the at least one air valve 21 and/or the at least one flood port 23 to thereby adjust the depth of the underwater buoyancy apparatus 5 in response to the velocity data.

The nautical system may further comprise an accelerometer or acceleration sensor 37, such as an underwater buoyancy apparatus vertical acceleration sensor for sensing the vertical acceleration of the underwater buoyancy apparatus 5. The underwater buoyancy apparatus vertical acceleration sensor 37 is preferably capable of sending a data signal to the depth control processor, which data signal provides vertical acceleration data of the underwater buoyancy apparatus 5 to the depth control processor. The depth control processor may then send a command signal, in response to the vertical acceleration data signal, to the at least one air valve 21 and/or the at least one flood port 23 to thereby adjust the depth of the underwater buoyancy apparatus 5 in response to the acceleration data.

The nautical system preferably further comprises a locking sheave system 35, through which the at least one tether 13 of the nautical system is routed such that various components of the nautical system 1 attached to the at least one tether 13 are slidably connected. The locking sheave system 35 is preferably capable of locking to and unlocking from at least one tether 13 of the nautical system 1 at adjustable positions along the at least one tether 13, such that the distances between selected components of the nautical system 1 are slidably adjustable. The locking to and unlocking from the at least one tether 13 preferably allows for an increasing or decreasing of the tethered distance between such components of the nautical system. In one preferred embodiment, the locking and unlocking of the locking sheave system 35 serves to slidably adjust the distance between the underwater buoyancy apparatus 5 and the sonar device 7. In another preferred embodiment, the locking and unlocking of the locking sheave system 35 serves to maintain a substantially fixed distance between the sonar device 7 and the underwater buoyancy apparatus 5.

The locking sheave system 35 preferably comprises at least one mechanical lockable sheave mechanism, a brake assembly, and/or a pulley or series of pulleys with lockable shafts, such that at least one tether 13 of the nautical system is routed through the locking sheave system 35, thereby slidably connecting the locking sheave system 35 to the at least one tether 13. The locking sheave system 35 preferably locks and/or unlocks in response to a signal from the control arrangement 25.

In one preferred embodiment, a locking sheave system is positioned between the nautical platform 3 and the underwater buoyancy apparatus 5. In one preferred embodiment, a locking sheave system 35 is physically attached to the housing underwater buoyancy apparatus 5 at a tether connection point 19. In fact, the locking sheave system may be an integral component of such a tether connection point.

Multiple locking sheave systems may be present at various locations of the nautical system 1. In one embodiment, at least one tether 13 between the nautical platform 3 and the underwater buoyancy apparatus 5 is routed through a first locking sheave system 35 present between the nautical platform and the underwater buoyancy apparatus 5, and at least one tether 13 is routed through a second locking sheave system 35 between the underwater buoyancy apparatus 5 and the sonar device 7.

The present invention further provides a method for adjusting the position of an underwater sonar device 7 within a body of water 9. According to this method, a nautical system 1 as described above is deployed into a body of water 9 such as an ocean, sea, lake, river, bay, gulf, reservoir, canal, pond, pool, or any other natural or manmade body of water. Once in the body of water 9, various components of the nautical system 1 sink to various depths within the water. It is preferred that the underwater buoyancy apparatus 5 reaches a depth at or below the depth of the nautical platform 3, and the underwater sonar device 7 reaches a depth at or below the depth of the underwater buoyancy apparatus 5. The depth of the underwater buoyancy apparatus 5 of the nautical system may be adjusted, either automatically or controllably, to thereby compensate for any effects that movement of the water surface may have on the nautical platform and/or other components of the nautical system 1. The depth of the underwater buoyancy apparatus 5 may be controllably adjusted by causing a lowering or raising the underwater buoyancy apparatus 5 within the body of water 9. In lowering the underwater buoyancy apparatus 5 within the body of water 9, air is released from within the buoyancy chamber 17 via the at least one air valve 21, and water is taken into the buoyancy chamber 17 via the at least one flood port 23. In raising the underwater buoyancy apparatus 5 within the body of water 9, air is taken into the buoyancy chamber 17 via the at least one air valve 21, water is released from within the buoyancy chamber 17 via the at least one flood port 23.

Upon deployment of the nautical system 1, it is preferred that a tether 13 connecting the underwater buoyancy apparatus 5 and the sonar device 7 is locked via the locking sheave system 35, thereby maintaining a fixed tether length between the underwater buoyancy apparatus 5 and the sonar device 7. Once within the body of water 9, at least one air valve 21 and/or at least one flood port 23 of the underwater buoyancy apparatus 5 allow air and/or water into the inner buoyancy chamber 17 such that the underwater buoyancy apparatus 5 reaches a targeted depth within the body of water 9. The inner buoyancy chamber 17 preferably accepts sufficient amounts of air and/or water such that the underwater buoyancy apparatus 5 maintains a substantially fixed depth at this position within the body of water 9. In one preferred embodiment, the targeted depth of the underwater buoyancy apparatus 5 comprises a specific ordered depth which may be pre-determined and/or pre-selected, prior to deployment, by a human user or a computer such as a computer processor of the depth control processor. The selected ordered depth of the underwater buoyancy apparatus 5 is reached by controlling the amounts of air and/or water present within the inner buoyancy chamber 17. The amounts of air and/or water within the inner buoyancy chamber 17, and the flow of such air and/or water into and out of the inner buoyancy chamber 17, are preferably controlled by the control arrangement 25, as described above. In an alternate embodiment, the targeted depth of the underwater buoyancy apparatus 5 is not pre-determined or pre-selected, but rather is determined and/or selected during or after deployment of the nautical system 1 into the body of water 9. In this embodiment, the targeted depth is determined and/or selected in consideration of the position and movement of the nautical platform 3 and/or other components of the nautical system 1 within the body of water 9 during or after deployment.

Preferably, an underwater buoyancy apparatus depth sensor 31 senses when the underwater buoyancy apparatus 5 has reached its targeted depth. A signal is then sent from the underwater buoyancy apparatus depth sensor 31 to the depth control processor, which in turn sends a signal instructing the locking sheave system 35 to disengage and unlock from the at least one tether 13. This allows at least a portion of the at least one tether 13 between the underwater buoyancy apparatus 5 and the sonar device 7 to pay out until the sonar device 7 reaches its targeted depth. In one preferred embodiment, the targeted depth of the underwater sonar device 7 comprises a specific ordered depth which may be pre-determined and/or pre-selected, prior to deployment, by a human user or a computer such as a computer processor of the depth control processor. In an alternate embodiment, the targeted depth of the sonar device is not pre-determined or pre-selected, but rather is determined and/or selected during or after deployment of the nautical system 1 into the body of water 9. In this embodiment, the targeted depth is determined and/or selected in consideration of the position and movement of the nautical platform 3, the underwater buoyancy apparatus 5, and/or other components of the nautical system 1 within the body of water 9 during or after deployment.

A sonar device depth sensor 33 then senses when the sonar device 7 has reached its targeted depth. A signal is then sent from the sonar device depth sensor 33 to the depth control processor, which in turn sends a signal instructing the locking sheave system 35 to engage and lock to the at least one tether 13. At this point the sonar device 7 is preferably suspended from and supported by the underwater buoyancy apparatus 5. The at least one tether 13 between the nautical platform 3 and the underwater buoyancy apparatus 5 is preferably allowed to go sufficiently slack such that horizontal and/or vertical motions of the nautical platform 3 do not impart substantial vertical or horizontal forces to the underwater buoyancy apparatus 5. Thus, the underwater buoyancy apparatus 5 and sonar device 7 are separated from any wave induced vertical and/or horizontal motion of the nautical platform 3.

If a change in depth of the sonar device 7 is desired, the lockable sheave system 35 is unlocked in response to a signal from the control arrangement 25, and the sonar device 7 is raised or lowered. With the lockable sheave system 35 unlocked, the at least one tether 13 is allowed to pass freely through a tether connection point 19 of underwater buoyancy apparatus 5, to a fixed tether connection point 29 on the sonar device 7. In one preferred embodiment, the sonar device 7 is raised or lowered to the new depth by means of a reel mechanism or the like of the nautical platform 3. The underwater buoyancy apparatus 5 preferably maintains substantially fixed depth within the body water 9 during this operation. The underwater buoyancy apparatus 5 preferably maintains this fixed depth by taking in water via the at least one flood port 23, as described above, to counteract any upward movement caused by the loss of the sonar device's weight, as that weight is taken up by the nautical platform 3 via the at least one tether 13. When the sonar device 7 reaches its new targeted depth as sensed by a sonar device depth sensor 33, a signal is sent from the sonar device depth sensor 33 to the depth control processor, which in turn sends a signal instructing the locking sheave system 35 to engage. This locks the at least one tether 13, thus locking the underwater buoyancy apparatus 5 to the sonar device 7 again.

During operation of the nautical system 3, the depth control system preferably monitors any deviation or “depth error” (DE) between the ordered depth and actual depth of the underwater buoyancy apparatus 5. Once an ordered depth is selected, control band or “control depth zone” is determined, preferably by the depth control system. The control depth zone is an area of acceptable depth deviation of the underwater buoyancy apparatus 5 within the body of water 9. Should the underwater buoyancy apparatus 5 deviate from its desired depth, a depth error (DE) is sensed by an underwater buoyancy apparatus depth sensor 31. Should this deviation fall outside of the control depth zone, a corresponding depth error signal is sent to the depth control processor. The depth control processor then preferably responds to counteract the deviation by raising or lowering the underwater buoyancy apparatus 5 as described above. Preferably, the depth control processor sends a command signal, in response to the depth error signal, which is sent to and applied to the at least one air valve 21 and/or the at least one flood port 23 to thereby adjust the depth of the sonar device 7, as described above, such that the underwater buoyancy apparatus 5 within the body of water 9 maintains a depth within the control depth zone.

The depth error (DE) is preferably calculated using the formula: DE=f _(A) A+f _(V) V+f _(D)(D _(O) −D _(S))+f _(Q) Q

-   -   wherein:         -   DE is the calculated depth error         -   A is the sensed vertical acceleration of the underwater             buoyancy apparatus;         -   V is the sensed vertical velocity of the underwater buoyancy             apparatus;         -   D_(O) is the ordered depth of the underwater buoyancy             apparatus;         -   D_(S) is the sensed depth of the underwater buoyancy             apparatus, as sensed by an underwater buoyancy apparatus             depth sensor;         -   Q is a damping factor, determined to provide a time delay             between the receipt of the depth error signal and the             generation of a corresponding command signal;         -   f_(A) is an empirically determined control response factor,             said determined such that a sensed vertical acceleration (A)             results in an appropriate calculated depth error,         -   f_(V) is an empirically determined control response factor,             determined such that a sensed vertical velocity (V) results             in an appropriate calculated depth error,         -   f_(D) is an empirically determined control response factor,             determined such that a difference between sensed depth             (D_(S)) and ordered depth (D_(O)) results in an appropriate             calculated depth error; and         -   f_(Q) is an empirically determined control response factor,             determined such that the damping factor (Q) results in an             appropriate calculated depth error.

A block diagram of a buoyancy control algorithm of the present invention. is shown in FIG. 2. According to FIG. 2, the damping factor, Q, is obtained by calculating the first differential of the sensed acceleration with respect to time. To this value is added a factor consistent with the position of the at least one air valve, preferably at least one vent valve and at least one blow valve. This factor serves to dampen system response during blowing and venting operations, to minimize depth oscillations.

Using acceleration, velocity, and damping in the calculation of depth error, the underwater buoyancy apparatus's velocity and acceleration are controlled such that the depth control function is responsive to changes in movement, such as vertical forces and/or horizontal forces acting on the underwater buoyancy apparatus in a manner such that the actual depth of the underwater buoyancy apparatus is substantially maintained at or near the ordered depth with a minimum of vertical motion.

The system response factors, f_(A), f_(V), f_(D), and f_(Q), are determined empirically such that each sensed parameter—acceleration, velocity, depth, and dampening— is modified to respond correctly. The system responds differently with the sonar device attached, that is with the locking sheave system locked, than it responds when the sonar device is not attached, that is with the locking sheave system unlocked. This is because the buoyancy chamber is supporting a different weight in each of the two conditions such that a constant amount of control signal would result in different system responses. To counter this, the depth control processor is preferably capable of calculating a system response factor upon receiving a signal that the locking sheave system is or is not locked, meaning that the sonar device is or is not attached. In accordance with this invention, various calculations may be conducted by the depth control processor such that other system response factors may be determined for various circumstances. In one embodiment, a control function is determined for slowing an error response to minimize depth oscillations.

Once calculated, if the DE value is within a control depth zone, a command signal is sent from depth control processor which causes a shutting of the at least one air valve 21. If the DE value is positive, and outside the control depth zone, a command signal is sent from depth control processor which causes the at least one air valve 21 to release air, thus the lowering of the underwater buoyancy apparatus 5, as described above, until the calculated DE value indicates that the underwater buoyancy apparatus 5 has returned to the control depth zone. If the DE value is negative, and outside the control depth zone, a command signal is sent from depth control processor which causes the at least one air valve 21 to take air in, thus raising the underwater buoyancy apparatus 5, as described above, until the calculated DE value is returned to the control depth zone.

Furthermore, the invention provides a method for the emergency recovery of the underwater buoyancy apparatus 5 and sonar device 7, for circumstances such as wherein the sonar device 7 may be damaged, lost at sea or become otherwise unattached.

According to this embodiment, a nautical system 1 as described above is deployed into a body of water 9. The nautical system 1 preferably comprises a depth control system further comprising a tether connection sensor as described above. The tether connection sensor senses break or other loss in continuity of a tether connection between the nautical platform 3 and the sonar device 7. The tether connection sensor sends a signal to the depth control processor, which then sends a first command signal to thereby lock the locking sheave system, thereby locking the underwater buoyancy apparatus 5 to the nautical platform 3 via at least one tether 13. The depth control processor then sends a second command signal to the at least one air valve 21 and/or the at least one flood port 23, such that air is taken into the buoyancy chamber 17 via the at least one air valve 21, and water is released from within the buoyancy chamber 17 via the at least one flood port 23 as described above. The decrease of water within the inner buoyancy chamber 17 and the increase of air within the inner buoyancy chamber 17 causes the underwater buoyancy apparatus 5 to thus be raised within the body of water 9. In one preferred embodiment, the underwater buoyancy apparatus 5 is raised at least to the depth of the nautical platform 3. Preferably the underwater buoyancy apparatus 5 is raised to the surface of the body of water 9, where emergency recovery procedures may be performed and/or subsequent deployment of the underwater buoyancy apparatus 5 may be conducted.

While the present invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto. 

1. A nautical system comprising; a) a nautical platform adapted for positioning on or within a body of water; b) an underwater buoyancy apparatus connected to the nautical platform via at least one tether, which underwater buoyancy apparatus comprises: a housing defining an inner buoyancy chamber, which buoyancy chamber is capable of containing a volume of air and/or water, and wherein the housing comprises at least one air valve capable of allowing air into and/or out of the inner buoyancy chamber and at least one flood port capable of allowing water into and/or out of the inner buoyancy chamber; c) an underwater sonar device connected to the underwater buoyancy apparatus via at least one tether, such that a distance between the underwater buoyancy apparatus and the sonar device is adjustable, which sonar device is capable of transmitting and/or receiving acoustic sonar signals; and d) a control arrangement for controlling the at least one valve and/or the at least one flood port of the underwater buoyancy apparatus.
 2. The nautical system of claim 1 wherein the at least one tether is sufficiently slack between the nautical platform and the underwater buoyancy apparatus such that a horizontal and/or vertical motion of the nautical platform does not impart a substantial vertical or horizontal force to the underwater buoyancy apparatus.
 3. The nautical system of claim 1 wherein the underwater buoyancy apparatus is slidably connected along at least one tether between the nautical platform and the sonar device.
 4. The nautical system of claim 1 wherein the at least one tether between the nautical platform and the underwater buoyancy apparatus is continuous with the at least one tether between the underwater buoyancy apparatus and the underwater sonar device.
 5. The nautical system of claim 1 wherein the at least one tether between the nautical platform and the underwater buoyancy apparatus is not continuous with the at least one tether between the underwater buoyancy apparatus and the underwater sonar device.
 6. The nautical system of claim 1 wherein the underwater buoyancy apparatus comprises an air controller for the at least one air valve for controlling a flow of air into and/or out of the inner buoyancy chamber.
 7. The nautical system of claim 1 wherein the underwater buoyancy apparatus comprises a water controller for the at least one flood port for controlling a flow of water into and/or out of the inner buoyancy chamber.
 8. The nautical system of claim 1 wherein the at least one air valve comprises a vent valve capable of expelling air from the buoyancy chamber.
 9. The nautical system of claim 1 wherein the at least one air valve comprises a blow valve capable of injecting air into the buoyancy chamber.
 10. The nautical system of claim 9 further comprising an air source.
 11. The nautical system of claim 1 wherein the control arrangement comprises a depth control system comprising: a) an underwater buoyancy apparatus depth sensor for sensing the depth of the underwater buoyancy apparatus and an underwater sonar device depth sensor for sensing the depth of the underwater sonar device and which underwater buoyancy apparatus depth sensor and sonar device depth sensor are each capable of sending a data signal to a depth control processor, which data signal provides depth and/or position data of the underwater buoyancy apparatus and the underwater sonar device, respectively, to a depth control processor; and b) a depth control processor capable of sending and receiving data signals and/or action signals to and from the underwater buoyancy apparatus depth sensor, the sonar device depth sensor, the at least one air valve, and/or the at least one flood port, and which depth control processor is further capable of controlling the at least one air valve and/or the at least one flood port.
 12. The nautical system of claim 11 which further comprises at least one tether connection sensor capable of sensing a break in a tether connection between the nautical platform and the sonar device.
 13. The nautical system of claim 11 which further comprises an underwater buoyancy apparatus vertical velocity sensor far sensing the vertical velocity of the underwater buoyancy apparatus, which underwater buoyancy apparatus vertical velocity sensor is capable of sending a data signal to the depth control processor, which data signal provides vertical velocity data of the underwater buoyancy apparatus to the depth control processor.
 14. The nautical system of claim 11 which further comprises an underwater buoyancy apparatus vertical acceleration sensor for sensing the vertical acceleration of the underwater buoyancy apparatus, which underwater buoyancy apparatus vertical acceleration sensor is capable of sending a data signal to the depth control processor, which data signal provides vertical acceleration data of the underwater buoyancy apparatus to the depth control processor.
 15. The nautical system of claim 1 which further comprises a locking sheave system through which the at least one tether is routed, which locking sheave system is positioned between the nautical platform and the underwater buoyancy apparatus, which locking sheave system is capable of locking to and unlocking from the at least one tether at adjustable positions along the at least one tether to thereby maintain a substantially fixed distance between the sonar device and the underwater buoyancy apparatus, and/or adjust the distance between the underwater buoyancy apparatus and the sonar device.
 16. An underwater buoyancy apparatus comprising a housing defining an inner buoyancy chamber, which buoyancy chamber is capable of containing a volume of air and/or water, and wherein the housing comprises at least one air valve capable of allowing air into and/or out of the inner buoyancy chamber and at least one food port capable of allowing water into and/or out of the inner buoyancy chamber; which underwater buoyancy apparatus further comprises at least one tether for connecting the underwater buoyancy apparatus to a nautical platform; and which underwater buoyancy apparatus further comprises at least one tether for connecting the underwater buoyancy apparatus to an underwater sonar device such that a distance between the underwater buoyancy apparatus and the underwater sonar device is adjustable.
 17. The underwater buoyancy apparatus of claim 16 wherein the control arrangement comprises a depth control system comprising: a) an underwater buoyancy apparatus depth sensor for sensing the depth of the underwater buoyancy apparatus is capable of sending a data signal to a depth control processor, which data signal provides depth and/or position data of the underwater buoyancy apparatus to a depth control processor; and b) a depth control processor capable of sending and receiving data signals and/or action signals to and from the underwater buoyancy apparatus depth sensor, the at least one air valve, and/or the at least one flood port, and which depth control processor is further capable of controlling the at least one air valve and/or the at least one flood port.
 18. The underwater buoyancy apparatus of claim 17 further comprising an underwater buoyancy apparatus vertical velocity sensor for sensing the vertical velocity of the underwater buoyancy apparatus, which underwater buoyancy apparatus vertical velocity sensor is capable of sending a data signal to the depth control processor, which data signal provides vertical velocity data of the underwater buoyancy apparatus to the depth control processor.
 19. The underwater buoyancy apparatus of claim 17 further comprising an underwater buoyancy apparatus vertical acceleration sensor for sensing the vertical acceleration of the underwater buoyancy apparatus, which underwater buoyancy apparatus vertical acceleration sensor is capable of sending the data signal to a depth control processor, which data signal provides vertical acceleration data of the underwater buoyancy apparatus to the depth control processor.
 20. The underwater buoyancy apparatus of claim 16 which further comprises a locking sheave system through which the at least one tether is routed, which locking sheave system is capable of locking to and unlocking from the at least one tether at adjustable positions along the at least one tether.
 21. A method for adjusting the position of an underwater sonar device which comprises: I) deploying a nautical system into a body of water, which nautical system comprises: a) a nautical platform adapted for positioning on or within a body of water; b) an underwater buoyancy apparatus connected to the nautical platform via at least one tether, which underwater buoyancy apparatus comprises: a housing defining an inner buoyancy chamber, which buoyancy chamber is capable of containing a volume of air and/or water, and wherein the housing comprises at least one air valve capable of allowing air into and/or out of the inner buoyancy chamber and at least one flood port capable of allowing water into and/or out of the inner buoyancy chamber; c) an underwater sonar device connected to the underwater buoyancy apparatus via at least one tether, such that a distance between the underwater buoyancy apparatus and the sonar device is adjustable, which sonar device is capable of transmitting and/or receiving acoustic sonar signals; and d) a control arrangement for controlling the at least one valve and/or the at least one flood port of the underwater buoyancy apparatus; II) accepting sufficient amounts of air and/or water into the inner buoyancy chamber such that underwater buoyancy apparatus maintains a substantially fixed depth within the body of water; and III) controllably adjusting the depth of the underwater buoyancy apparatus to thereby compensate for the effects of movement of the nautical platform on the underwater sonar device by conducting at least one of steps (i) and (ii): i) lowering the underwater buoyancy apparatus within the body of water, by releasing air from within the buoyancy chamber via the at least one air valve, and taking water into the buoyancy chamber via the at least one flood port; and/or ii) raising the underwater buoyancy apparatus within the body of water, by taking air into the buoyancy chamber via the at least one air valve, and releasing water from within the buoyancy chamber via the at least one flood port.
 22. The method of claim 21 wherein the control arrangement comprises a depth control system comprising: a) an underwater buoyancy apparatus depth sensor for sensing the depth of the underwater buoyancy apparatus and an underwater sonar device depth sensor for sensing the depth of the underwater sonar device and which underwater buoyancy apparatus depth sensor and sonar device depth sensor are each capable of sending a data signal to a depth control processor, which data signal provides depth and/or position data of the underwater buoyancy apparatus and the underwater sonar device, respectively, to a depth control processor; and b) a depth control processor capable of sending and receiving data signals and/or action signals to and from the underwater buoyancy apparatus depth sensor, the sonar device depth sensor, the at least one air valve, and/or the at least one flood port, and which depth control processor is further capable of controlling the at least one air valve and/or the at least one flood port; wherein the underwater buoyancy apparatus depth sensor sends a depth data signal to the depth control processor, which depth control processor receives the depth data signal and sends an action signal, in response to the depth data signal, to the at least one air valve and/or the at least one flood port to thereby adjust the depth of the underwater buoyancy apparatus according to step (III).
 23. The method of claim 22 wherein the nautical system further comprises an underwater buoyancy apparatus vertical velocity sensor for sensing the vertical velocity of the underwater buoyancy apparatus, which underwater buoyancy apparatus vertical velocity sensor is capable of sending a data signal to the depth control processor, which data signal provides vertical velocity data of the underwater buoyancy apparatus to the depth control processor, and which depth control processor receives the vertical velocity data signal and sends a command signal, in response to the vertical velocity data signal, to the at least one air valve and/or the at least one flood port to thereby adjust the depth of the underwater buoyancy apparatus according to step (III).
 24. The method of claim 22 wherein the nautical system further comprises an underwater buoyancy apparatus vertical acceleration sensor for sensing the vertical acceleration of the underwater buoyancy apparatus, which underwater buoyancy apparatus vertical acceleration sensor is capable of sending a data signal to the depth control processor, which data signal provides vertical acceleration data of the underwater buoyancy apparatus to the depth control processor, which depth control processor receives the vertical acceleration data signal and sends a command signal, in response to the vertical acceleration data signal, to the at least one air valve and/or the at least one flood port to thereby adjust the depth of the underwater buoyancy apparatus according to step (III).
 25. The method of claim 22 which further comprises a locking sheave system through which the at least one tether is routed, which locking sheave system is positioned between the nautical platform and the underwater buoyancy apparatus, which locking sheave system is capable of locking to and unlocking from the at least one tether at adjustable positions along the at least one tether to thereby maintain a substantially fixed distance between the sonar device and the underwater buoyancy apparatus, and/or adjust the distance between the underwater buoyancy apparatus and the sonar device; wherein the locking sheave system locks and/or unlocks in response to a signal from the depth control processor to thereby adjust the depth of the underwater buoyancy apparatus according to step (III).
 26. The method of claim 22 which comprises the steps of: selecting an ordered depth of the underwater buoyancy apparatus; determining a control depth zone adjacent to the ordered depth, sending a depth signal from the underwater buoyancy apparatus depth sensor to the depth control processor, determining a depth error if the underwater buoyancy apparatus reaches a depth within the body of water which depth is outside the control depth zone.
 27. The method of claim 26 further comprising the steps of: sending a command signal, in response to the depth error signal, from the depth control processor to the at least one air valve and/or the at least one flood port, to thereby adjust the depth of the sonar device according to step (III) such that the underwater buoyancy apparatus within the body of water maintains a depth within the control depth zone.
 28. The method of claim 26 wherein the depth error value is calculated by the formula: DE=f _(A) A+f _(V) V+f _(D)(D _(O) −D _(S))+f _(Q) Q wherein: DE is a calculated depth error; A is a sensed vertical acceleration of the underwater buoyancy apparatus; V is a sensed vertical velocity of the underwater buoyancy apparatus, D_(O) is an ordered depth of the underwater buoyancy apparatus; D_(S) is a sensed depth of the underwater buoyancy apparatus, as sensed by the underwater buoyancy apparatus depth sensor; Q is a damping factor, said damping factor being determined to provide a time delay between the depth signal exceeding a depth control band and the generation of a command signal; f_(A) is an empirically determined control response factor, said factor determined such that a sensed vertical acceleration (A) results in a calculated depth error; f_(V) is an empirically determined control response factors, said factor determined such that a sensed vertical velocity (V) results in a calculated depth error; f_(D) is an empirically determined control response factors, said factor determined such that a difference between sensed depth (D_(S)) and ordered depth (D_(O)) results in a calculated depth error; and f_(Q) is an empirically determined control response factor, said factor determined such that a damping factor (Q) results in a calculated depth error.
 29. The method of claim 21 wherein: the nautical system comprises group of sensors that sense the depth, vertical velocity, and vertical acceleration of the underwater buoyancy apparatus; step (II) comprises selecting a desired underwater buoyancy apparatus operating depth; step (III) comprises determining a control function for slowing an error response to minimize depth oscillations; and step (III) comprises an algorithm for calculating a depth error signal; whereby the depth error signal is applied to the control valves in a manner such that water is forced out of or flooded into the underwater buoyancy apparatus to maintain its depth within a controlled depth band.
 30. The method of claim 21 wherein the at least one air valve comprises at least one vent valve capable of releasing air from within the buoyancy chamber to thereby lower the underwater buoyancy apparatus within the body of water, and/or at least one blow valve capable taking air into the buoyancy chamber via an air source to thereby raise the underwater buoyancy apparatus within the body of water.
 31. A method for the emergency recovery of an underwater buoyancy apparatus and a sonar device which arc part of a nautical system, the method comprising; I) deploying a nautical system into a body of water, which nautical system comprises: a) a nautical platform adapted for positioning on or within a body of water; b) an underwater buoyancy apparatus connected to the nautical platform via at least one tether, which underwater buoyancy apparatus comprises: a housing defining an inner buoyancy chamber, which buoyancy chamber is capable of containing a volume of air and/or water, and wherein the housing comprises at least one air valve capable of allowing air into and/or out of the inner buoyancy chamber and at least one flood port capable of allowing water into and/or out of the inner buoyancy chamber; c) an underwater sonar device connected to the underwater buoyancy apparatus via at least one tether, such that a distance between the underwater buoyancy apparatus and the sonar device is adjustable, which sonar device is capable of transmitting and/or receiving acoustic sonar signals; and d) a control arrangement for controlling the at least one valve and/or the at least one flood port of the underwater buoyancy apparatus; and e) a tether connection sensor capable of sensing a loss of tether continuity between the nautical platform and the sonar device; and f) a depth control system comprising: i) an underwater buoyancy apparatus depth sensor for sensing the depth of the underwater buoyancy apparatus and an underwater sonar device depth sensor for sensing the depth of the underwater sonar device and which underwater buoyancy apparatus depth sensor and sonar device depth sensor are each capable of sending a data signal to a depth control processor, which data signal provides depth and/or position data of the underwater buoyancy apparatus and the underwater sonar device, respectively, to a depth control processor; and ii) a depth control processor capable of sending and receiving data signals and/or action signals to and from the underwater buoyancy apparatus depth sensor, the sonar device depth sensor, the at least one air valve, and/or the at least one flood port, and which depth control processor is further capable of controlling the at least one air valve and/or the at least one flood port; and g) a locking sheave system through which the at least one tether is routed, which locking sheave system is positioned between the nautical platform and the underwater buoyancy apparatus, which locking sheave system is capable of locking to and unlocking from the at least one tether at adjustable positions along the at least one tether to thereby maintain a substantially fixed distance between the sonar device and the underwater buoyancy apparatus, and/or adjust the distance between the underwater buoyancy apparatus and the sonar device; II) generating a first command signal from the depth control system, in response to a loss of tether continuity signal from the tether connection sensor, such that the locking sheave system locks; III) generating a second command signal from the depth control system, thereby directing the opening of the at least one air valve of the underwater buoyancy apparatus in response to a loss of tether continuity signal; and IV) controllably forcing air into the underwater buoyancy apparatus such that underwater buoyancy apparatus is raised to the surface of the body of water in response to the loss of tether continuity signal. 